Sorry I re-read your first post and see it is both fronts locking up. So it still could be the master Cyl. adjustment among other things. A proportioning valve can be just that OR a proportioning valve and residual all in one together. Like already said I don't see why you need to duplicate the residual part. Still would check master cyl. and make sure it's for disc drums with no resid built in, I have been sent the wrong one on several occasions. Lon